In typical commercial reproduction apparatus (electrostatographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged dielectric member. Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric member. A receiver member is then brought into contact with the dielectric member. An electric field, such as provided by a corona charger or an electrically biased roller, is applied to transfer the marking particle developed image to the receiver member from the dielectric member. After transfer, the receiver member bearing the transferred image is separated from the dielectric member and transported away from the dielectric member to a fuser apparatus at a downstream location. There the image is fixed to the receiver member by heat and/or pressure from the fuser apparatus to form a permanent reproduction thereon.
One type of fuser apparatus, utilized in typical reproduction apparatus, includes at least one heated roller and at least one pressure roller in nip relation with the heated roller. The fuser apparatus rollers are rotated to transport a receiver member, bearing a marking particle image, through the nip between the rollers. The pigmented marking particles of the transferred image on the surface of the receiver member soften and become tacky in the heat. Under the pressure, the softened tacky marking particles attach to each other and are partially imbibed into the interstices of the fibers at the surface of the receiver member. Accordingly, upon cooling, the marking particle image is permanently fixed to the receiver member.
When the reproduction apparatus is in the standby mode between job runs, the heated fuser roller will be in a substantially equilibrium condition; that is, there is at most only a small temperature gradient between the outer surface of the fuser roller and the inner core. Then when the job run begins energy (heat) is removed from the fuser roller to the copies being fused. As a result, the temperature at the outer surface of the fuser roller droops very quickly. Since the temperature droops from the operating setpoint, the logic and control for the reproduction apparatus turns on the fuser heating device. However, depending upon the thickness of the fuser roller, there is a time lag until the fuser roller surface receives enough energy to get back to the desired fusing temperature. During the time lag, the droop in surface temperature causes inferior fusing quality. When the reproduction apparatus is a process color machine, the temperature droop results in objectionable lower saturation of colors and image gloss.
To overcome fuser roller temperature droop at the start of a reproduction run, some apparatus include temperature control algorithms that raise the fuser roller temperature at the start of the run above the run temperature set point. That is, the energy input is started earlier so that the temperature droop from the setpoint is minimized. However, this causes the fuser roller temperature to be higher at the start of a job run than the desired setpoint and lower at the bottom of the temperature droop. Therefore, the copies over a job run will be fused at differing temperatures and have differing image quality appearance.